This invention relates generally to flow sensors for monitoring the volume and rate of fluid flow through a fluid flow path and, more particularly, to miniature flow sensors configured to be implanted in a human body for measurement of blood flow within the circulatory system.
It has been known in the past that fluid flow through a tubular flow path can be measured using an electrical heater and a pyroelectric detector that are mounted on the outside of the flow path. The heater heats the fluid and the pyroelectric detector detects the resulting temperature change as the fluid flows through the fluid path. However, in many cases, such flow sensors cannot sense the direction of fluid flow and can erroneously consider a negative fluid flow to be a positive fluid flow.
Flow sensors may be incorporated into an implantable medical device such as a cardiac pacemaker by sizing the sensors to have a sufficiently small diameter. However, the small size of these sensors requires the heater and the detector, and their associated electrical conductors, to be in close proximity. Conductors in close proximity tend to induce unwanted signals upon each other that may interfere with the proper monitoring of the fluid flow. The proper operation of certain critical medical devices, such as cardiac pacemakers, renders unacceptable flow sensors that can generate unwanted or stray electrical signals.
Accordingly, there exists a need for an implantable flow sensor and related readout circuitry that is sensitive over a wide range of fluid flow rates and that does not produce unwanted or stray electrical signals when implanted in the body. There also exists a need for an implantable flow sensor that provides an indication of the fluid flow direction. The present invention satisfies these needs.